Superintendent William Hite says of 54 high schools only three do not use them, and it's a matter of consistency.
"Metal detectors are intended to keep everyone in the building safe. Students and staff must know there are intentional levels of protection in their schools that they can rely on," Hite said.
Some students, including Nayeli Perez from the Academy at Palumbo, made impassioned arguments against the devices.
"It wasn't until this year that I really asked myself why metal detectors are so commonplace nowadays. And in school, of all places. As if we're just criminals waiting to happen, and not just kids," Perez said.
Board member Chris McGinley said the policy was about protecting students.
"I, also as a principal, in an environment of trust with students I knew, on two occasions took loaded guns away from students," McGinley said.
The actual board went to a committee room and finished voting in private while streaming the proceedings online.